Food Quality and Preference 50 (2016) 145–151
Contents lists available at ScienceDirect
Food Quality and Preference
journal homepage: www.elsevier.com/locate/foodqual
Eating in the dark: A dissociation between perceived and actual food
consumption
Britta Renner a,⇑, Gudrun Sproesser a, F. Marijn Stok a, Harald Schupp b
a
b
Psychological Assessment & Health Psychology, Department of Psychology, University of Konstanz, Germany
General Psychology, Department of Psychology, University of Konstanz, Germany
a r t i c l e
i n f o
Article history:
Received 9 September 2015
Received in revised form 5 February 2016
Accepted 9 February 2016
Available online 10 February 2016
Keywords:
Blind
Sight
Food intake
Food perception
Eating
Food taste
Visual cues
Vision
a b s t r a c t
Objective: According to folk intuition ‘‘Eye appeal is half the meal,” raising the question how the absence
of vision or ‘visual flavor’ affects food perception, willingness to buy, and food intake. Method: In the present experiment, ninety students were assigned to either a blindfolded or a non-blindfolded condition
and completed a bogus ice cream taste test. Taste perceptions and purchase willingness were assessed
during tasting, and actual and perceived intake, afterward. Results: Blindfolded participants rated the
ice cream lower on hedonic but higher on ambiguity taste attributes. Although eating without vision
led to a lower purchase willingness and a 9% decrease in the actual intake, blindfolded participants overestimated their intake by 88% while non-blindfolded overestimated their intake only by 35%. Conclusions:
Thus, depriving participants of visual input dissociated perceived intake from actual intake. Shifting
attention toward interoceptive cues of eating may provide unobtrusive and naturalistic means to change
eating experiences.
Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction
Human eating behavior is a fascinating and complex system.
Most of the behavioral eating repertoire is not innate, and the system is highly adaptive to the environment. This becomes obvious
when we consider that human beings can adapt to eat virtually
anything. For example, mud or soil, which most human beings
would not consider as eatable, has recently become a special ingredient at some of Japan’s high-end restaurants. News outlets such as
CNN and The Japan Times featured chef Toshio Tanabe, the inventor of the new tsuchi ryōri (‘‘earth cuisine”) which includes courses
from appetizers to desserts that are based on real earth from the
ground (Swinnerton, 2013; Zolbert, 2013).
From this point of view, eating behavior can be conceptualized
as an embodied behavior system (Ghane & Sweeny, 2013). This
means that our behavioral eating responses, our thoughts, feelings,
and observable behavior related to food intake, are the result of
bodily interactions with the food environment. We react to food
based on our five senses, and vision is particularly important for
food choice and eating (see also Wadhera & Capaldi-Phillips,
2014). Folk wisdom tells us that ‘‘eye appeal is half the meal”,
⇑ Corresponding author at: Psychological Assessment and Health Psychology,
University of Konstanz, PO Box 47, D-78457 Konstanz, Germany.
E-mail address: [email protected] (B. Renner).
http://dx.doi.org/10.1016/j.foodqual.2016.02.010
0950-3293/Ó 2016 Elsevier Ltd. All rights reserved.
and scientific evidence confirms this idea. Visual cues determine
the hedonic appeal of food by triggering hedonic anticipations or,
as Spence and Piqueras-Fiszman (2012) have phrased it, they trigger the ‘visual flavor’. Thus, the visual system is key for physiological, emotional, and cognitive responses toward food (Schupp &
Renner, 2011; van der Laan, de Ridder, Viergever, & Smeets,
2011). In contrast, public health interventions often recommend
eating regulation strategies that rely on the cognitive system in
order to navigate the complex food environment. For example,
dietary guidelines or nutrition facts are rather abstract and cognitive; most people probably cannot see, smell, or taste a food when
presented with nutrition facts. Thus, knowing the nutrition facts
does not tell us which food it is and what it looks like, and whether
it is green or red, fluffy or mushy, aromatic or bland. Considering
this, the question arises whether food perception and eating
behavior change when consumers are sensorily deprived; that is,
what happens to our behavioral eating responses when we cannot
see the food we are eating?
Only a few studies have examined the impact of vision on eating behavior so far (see for an overview Spence & PiquerasFiszman, 2012; Wadhera & Capaldi-Phillips, 2014). In a first,
pioneering experimental study, Linné, Barkeling, Rössner, and
Rooth (2002) asked normal-weight participants to eat a set testmeal lunch once with and once without a blindfold. When blindfolded, participants ate 22% less food but felt just as satiated as
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B. Renner et al. / Food Quality and Preference 50 (2016) 145–151
when eating without a blindfold. A similar pattern was observed
within obese subjects eating a set lunch (Barkeling, Linné, Melin,
& Rooth, 2003) or breakfast (Burger, Fisher, & Johnson, 2011) with
an observed decrease in intake between 12% and 24% in the blindfolded compared to the non-blindfolded condition. Conversely,
Scheibehenne, Todd, and Wansink (2010) studied food intake
during a set lunch in a ‘‘dark” restaurant and found that (in the
so-called ‘‘regular portion size” condition) food intake was 6%
higher than when the restaurant was normally lit. However, people
tended to empty their plate: in the dark, participants ate 96% of the
amount served. This suggests that portion size was the leading cue
for consumption in the dark condition, resulting in a higher consumption overall compared to the normally lit condition (see also
Wansink, Shimizu, Cardello, & Wright, 2012).
In all previous studies, people received a complete meal. Since
people have a tendency to view the portion they are being served
as appropriate and normal, portion size norms (Burger et al., 2011;
Herman & Polivy, 2008; Scheibehenne et al., 2010) may have
affected the observed results. Likewise, the served complete meals
were intended as a free substitute for a regular meal; thus, financial concerns may have influenced the results. In order to decrease
the potential influence of portion size norms and financial concerns inherent in serving a complete substitute meal, the present
study used a taste test paradigm with several portions of one food
item (ice cream). Furthermore, Wansink and colleagues (2012)
suggested that vision deprivation might increase the perceived
ambiguity of the food, leading to a decrease in willingness to consume the food in the future. However, this contention has not
explicitly been investigated, yet.
Extending these meal-based studies examining the impact of
visual deprivation, the present study assessed, in addition to actual
food intake, also other outcome variables in order to shed more
light on the mechanisms. During the food intake session, taste
and texture perception as well as approach behavior such as willingness to buy the product indicating acceptance of the food sample were measured. We assessed taste perception ‘online’ – that is,
in real time during the food intake process – and not post-meal
(see for example Burger et al., 2011; Scheibehenne et al., 2010),
in order to reduce potential memory effects due to retrieving prior
experiences (see Robinson, 2014). Moreover, perceived food intake
was assessed indicating the ability to monitor food intake. Taken
together, we examined the effect of visual deprivation on four different response modes: (1) taste perceptions, for example, how
much participants like what they eat and whether they perceive
the food as ambiguous; (2) willingness to buy the product; (3)
intake behavior, i.e. how much participants actually eat; and (4)
the ability to monitor food intake, i.e. how much participants think
they eat.
2. Material and methods
2.1. Sample
Ninety participants from the University of Konstanz took part in
the experiment. No participant was excluded; however, the numbers of observations vary slightly due to missing values. List-wise
deletion per analysis was applied to handle missing data. Thus, if
any single value was missing, the case was excluded from analysis.
However, rate of missing data was low with a maximum of two
missing per variable. Participants were assigned to one of two
experimental conditions: blindfolded (n = 50) and nonblindfolded (n = 40). For practical reasons, the conditions were
not run simultaneously but one after the other on a rolling basis.
The non-blindfolded condition was run first. Participants had a
mean age of 22.5 years (SD = 4.1) and a mean body mass index
(BMI) of 21.8 kg/m2 (SD = 3.0). Sixty-two of the participants were
female (69%) and 28 were male (31%). For more details on participant characteristics see also Table S1 in the Supplementary Material available online. Participants received €8 for participation or
course credit.
2.2. Procedure and materials
Participants arrived at the laboratory with the understanding
that they would be taking part in a study about tasting. To decrease
possible differences in initial hunger level, we informed participants when they scheduled an appointment that they should
refrain from eating for two hours before participation.
The outside temperature was recorded as a control variable.
After giving informed consent, participants filled in a brief questionnaire assessing their demographics, baseline hunger (rated on
a 6-point scale ranging from 1 = very hungry to 6 = very satiated),
and general liking of the ice cream (‘‘I like ice cream” rated on a
4-point scale ranging from 1 = completely disagree to 4 = completely agree). Several additional variables were assessed at baseline.1 These variables are not the focus of the current paper and
are reported only in the interest of full disclosure. Afterward, actual
food intake was assessed by a bogus taste test (e.g., Sproesser,
Schupp, & Renner, 2014). Bogus taste tests assess actual consumption of foods, thereby omitting the bias of self-reports or retrospective memories of eating behavior (e.g., Evers, de Ridder, & Adriaanse,
2009).
Participants were provided with three individual-sized cups of
GrandessaÒ ice cream which is sold by retailers in Germany. Three
different popular flavors were presented to the participants: Amarena Cherry, Caramel, and Spaghetti (a typically German type of ice
cream which consists of vanilla ice cream pressed through a shape
to resemble the shape of cooked spaghetti and strawberry sauce to
simulate tomato sauce). Each cup weighed approximately 95 g,
equivalent to 188 kcal. A standard tea spoon accompanied each
of the three cups. Participants were asked to evaluate the taste
and texture of the ice cream as well as how much they liked it
by rating basic taste aspects including hedonic appeal, ambiguity,
naturalness, freshness, as well as texture and mouth feeling.
Specifically, the taste test included 17 questions per ice cream flavor aiming at a comprehensive evaluation of the ice creams (e.g.,
‘‘How much do you like this ice cream?” or ‘‘How surprising is
the taste of this ice cream?”) with a 4-point response scale ranging
from 1 (not at all) to 4 (very much; cf. Sproesser et al., 2014, see
also Evers et al., 2009 and Table S2 in the Supplementary Material
available online). As there were no a priori reasons to assume differences in taste ratings between the three ice creams, and as the
impact of the condition did not differ across the three flavors, taste
ratings were summarized across the three flavors for analyses. In
addition, willingness to purchase was measured separately for
each presented ice cream on a 4-point scale from 1 (very unlikely)
to 4 (very likely) and summarized across the three flavors for
analyses.
The three ice cream bowls were placed in a handcrafted wooden
mount. Participants were told to taste and eat as much as they
liked. For effective blindfolding, participants wore modified ski
goggles and a plastic cape to protect their clothing in case of spillage. Since blind-folded participants could not fill in the taste rating questionnaire, an audio questionnaire, programmed in
PresentationÒ, was implemented in this condition. Participants
could navigate the questions using foot pedals (start question,
stop) and answered the questions aloud. A microphone in the room
1
The other variables that were assessed at baseline were positive and negative
affect, trait motives for eating, external and internal influences on eating, and
tendency to eat when stressed.
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B. Renner et al. / Food Quality and Preference 50 (2016) 145–151
transmitted their responses to an adjacent room, where the experimenter recorded them in real time. The sessions were videotaped
(with participants’ consent). During the taste test, the experimenter left the room.
After 15 min, the experimenter returned and administered
another brief questionnaire that assessed perceived intake. To
assess perceived intake, participants were asked to rate their
intake in an open question format (‘‘How many grams of ice cream
X did you eat?”), and an anchor was presented stating that one
spoon typically contains 9 g of ice cream. Perceived consumption
for the three ice creams was added to establish a measure of total
perceived intake. In addition, trait variables such as restrained
eating (routine and compensatory restraint, Schembre, Green, &
Melanson,, 2009, rated on an 5-point scale ranging from 1 = does
not describe me at all to 5 = describes me completely) and subjective health (rated on an 5-point scale ranging from 1 = poor to
5 = excellent) were assessed (for more details, see Table S1 in the
Supplemental Material available online). Finally, each participant’s
height and weight were measured. Moreover, the experimenter
collected the bowls with food and weighed them in a separate
room. Actual consumption was computed by subtracting the
post-taste weight from the pre-taste weight for each of the three
ice cream bowls. The three amounts were then added to establish
a measure of total consumption.
The ethics committee of the University of Konstanz approved
the study protocol. The study was carried out in accordance with
the provisions of the World Medical Association Declaration of
Helsinki.
3. Results
3.1. Descriptive analyses
T-Tests showed that participants in the non-blindfolded and
blindfolded condition did not differ in age (22 vs. 23 years), BMI
(21.9 vs. 21.7 kg/m2), general liking of ice cream (3.7 vs. 3.6),
restrained eating (1.9 vs. 1.8 for routine restraint and 2.6 vs. 2.6
for compensatory restraint), or subjective health (4.0 vs. 4.0;
|t|’s 6 1.21, p’s P .228; details provided in Table S1 in the Supplementary Material available online). A significant difference
between the two groups was found for outside temperature,
t(88) = 2.61, p = .011, with a higher average outdoor temperature
for the non-blindfolded group (M = 13.90 °C, SD = 5.57) as compared to the blindfolded group (M = 9.82 °C, SD = 8.55). In addition,
the non-blindfolded group (M = 2.75, SD = 0.98) reported on average (nearly significantly) more pre-consumption hunger as compared to the blindfolded group (M = 3.20, SD = 1.14, t(88) = 1.98,
p = .051. Further analyses were therefore conducted to statistically
control for the influence of outside temperature and hunger.
3.2. Taste perceptions
In order to examine whether vision deprivation affects taste
perceptions, mean ratings between the two experimental conditions were compared. As Fig. 1 shows, both groups rated the ice
cream positively, and across the two groups, ratings differed
between the 17 taste ratings. For example, the ice cream was rated
higher on palatability than naturalness. Importantly, while the
blindfolded and non-blindfolded groups showed a similar overall
profile of the mean taste ratings, they nevertheless differed on
mean levels for specific taste ratings. A MANOVA including the
17 taste ratings and condition (non-blindfolded vs. blindfolded)
as between-subjects factor confirmed that there was a significant
multivariate effect: Hotelling’s T = 1.40, F(17, 64) = 5.27, p < .001,
gp2 = .583. Specifically, hedonic taste ratings such palatability were
boring
need get used to*
surprising*
sweet
12
11
10
9
8
7
Non Blindfolded
Blindfolded
palatable*
good+
unpleasant*
5
4
3
unique*
intensive
interesng*
creamy
refreshing*
melts in mouth
fresh*
ice crystals
natural*
arficial+
Fig. 1. Taste ratings (sum scores across three types of ice cream, potential range
between 3 and 12). + p 6 .10, ⁄ p < .05.
rated higher, t(87) = 2.03, p = .046, or, in the case of unpleasantness
(negatively scored) lower, by the non-blindfolded group compared
to the blindfolded group, t(88) = 2.25, p = .027. Moreover, the
non-blindfolded group believed that the ice cream tasted more
natural, t(87) = 2.36, p = .021 and they gave lower, albeit not significantly, ratings for artificiality, t(88) = 1.80, p = .076. Likewise, the
two freshness-related ratings were higher in the non-blindfolded
group than in the blindfolded group, t’s (88) P 3.23, p’s 6 .002.
Conversely, for ratings related to the ambiguity of the taste experience, such as surprise and the need to get used to the taste, the
blindfolded group gave higher mean ratings than the nonblindfolded group, t’s (88) P 3.59, p’s 6 .001. In a similar vein,
uniqueness of the taste was rated higher by the blindfolded group,
t(88) = 2.95, p = .004, and they also found the taste more interesting, t(87) = 2.28, p = .025. For texture-related taste ratings such as
creaminess, melting, and ice crystals, no significant group differences were found, t’s 6 1.45, p’s P .152. The other ratings also
did not differ significantly between the two groups, t’s 6 1.66,
p’s P .101. Exact means, standard deviations, p-values, and
Cohen’s d are provided in Table S2 in the Supplementary Material
available online.
3.3. Willingness to buy
In a subsequent t-test, the question of how vision deprivation
affects the willingness to buy the food product was examined.
The results show that the blindfolded group (M = 2.2, SD = 0.62)
was less willing to buy the served ice cream in the future as compared to the non-blindfolded group, (M = 2.5, SD = 0.51), t(88)
= 2.15, p = .034.
3.4. Actual and perceived intake
In subsequent analyses, it was examined how vision deprivation affects the actual amount of intake and the monitoring of
the intake (i.e., perceived consumption) that is whether the
discrepancy between actual and perceived intake differs across
participants in the non-blindfolded and blindfolded condition.
We conducted a two-way repeated measures ANOVA with type
of intake (actual intake in grams vs. perceived intake in grams)
as repeated measurement factor and condition (non-blindfolded
vs. blindfolded) as between-subjects factor. The main effect for
condition was not significant, which indicates that visual deprivation (non-blindfolded: M = 137 g, SE = 16.3 g; blindfolded:
B. Renner et al. / Food Quality and Preference 50 (2016) 145–151
M = 151 g, SE = 13.4 g, F(1, 82) = 0.48 p = .491, gp2 = .006), did not
affect food intake across perceived and actual intake. However, a
significant main effect for the type of intake emerged, F(1, 82)
= 32.16, p < .001, gp2 = .28, indicating that the actual intake
(M = 110 g, SE = 7.7 g) was significantly lower than the perceived
intake (M = 178 g, SE = 15.3 g). This main effect was further
qualified by a significant condition x type of intake interaction,
F(1, 82) = 4.47, p = .038, gp2 = .05.
The condition x type of intake interaction is further broken
down in Fig. 2. As Fig. 2 depicts, the non-blindfolded group actually
consumed 116 g (SE = 11.8 g) and the blindfolded group actually
consumed 105 g (SE = 9.7 g). Thus, the blindfolded group ate 9%
less ice cream than the non-blindfolded group, although this difference was not significant. Interestingly, for perceived consumption,
an inverted pattern of results emerged. The non-blindfolded group
believed that they had eaten on average 158 g (SE = 23.6 g), and the
blindfolded group thought that they consumed on average 197 g
(SE = 19.5 g). Most importantly, together, these results show that
the discrepancy between perceived and actual consumption was
much larger in the blindfolded group than in the non-blindfolded
group. Comparing the perceived and actual intake within the two
experimental conditions shows that participants in the nonblindfolded group significantly overestimated their intake by
35%, F(1, 82) = 5.32, p = .024, gp2 = .06. However, this overestimation effect was much more pronounced in the blindfolded group,
where participants overestimated their intake by 88%, F(1, 82)
= 37.42, p < .001, gp2 = .31.
220
Intake
Actual Perceived
200
180
160
Intake in Grams
148
140
120
100
80
60
40
20
0
Non-blindfolded
Blindfolded
Condion
Fig. 2. Consumed ice cream in grams in dependence of condition and type of intake.
Error bars indicate standard errors of the mean.
4. Discussion
3.5. Control analyses
Since the two groups differed regarding reported preconsumption hunger and measured outdoor temperature, additional control analyses were undertaken to ensure that the
obtained pattern of results could not be attributed to differences
in these variables. For this purpose, two ANCOVAs, with willingness to buy as dependent variable and condition (nonblindfolded vs. blindfolded) as between-subjects factor, were
conducted with hunger and outside temperature as covariate,
respectively. Both ANCOVAs yielded no significant effect for hunger or outdoor temperature, F’s(1, 87) < 0.108, p’s P .743. Moreover, the effect of condition with lower willingness to buy within
the blindfolded condition, was still significant after controlling
for hunger, F(1, 87) = 4.19, p = .04, or temperature, F(1, 87) = 3.91,
p = .05.
In addition, two-way repeated measure ANCOVAs were conducted with type of intake (actual intake in grams vs. perceived
intake in grams) as repeated measurement factor, condition
(non-blindfolded vs. blindfolded) as between-subjects factor, and
hunger as well as outside temperature as covariate, respectively.
Neither outdoor temperature nor hunger was significantly related
to type of intake, F’s(1, 81) 6 0.196, p’s P .659 for main effects and
F’s(1, 81) 6 .197, p’s P .658 for interaction effects. However, probably due to reduced power, the interaction terms between type of
intake (actual vs. perceived) and condition (blindfolded vs. nonblindfolded) did not reach the <.05 significance threshold in the
analyses including covariates, though the effect sizes remained virtually unchanged. Again, a greater overestimation was observed
within the blindfolded group (actual intake: 108.9 g vs. perceived
intake: 203.8 g) than in the non-blindfolded group (actual intake:
114.2 g vs. perceived intake: 158.9 g) when controlling for outside
temperature, F(1, 81) = 3.92, p = .051, gp2 = .05). Also, a greater
overestimation was observed within the blindfolded group (actual
intake: 106.3 g vs. perceived intake: 197.7 g) than in the nonblindfolded group (actual intake: 113.4 g vs. perceived intake:
157.2 g) when controlling for hunger, F(1, 81) = 3.90, p = .052,
gp2 = .05).
The present experiment examined the effects of visual deprivation on food perception and eating responses. The results showed
that participants were significantly less willing to buy the food
product and ate 9% less when blindfolded than when seeing
(although the latter results was not statistically significant). The
amount of intake reduction is slightly lower than in previous studies on normal-weight participants who were served a set lunch
(Barkeling et al., 2003; Linné et al., 2002) or breakfast (Burger
et al., 2011). This difference might be due to the type of eating
situation (taste test vs. full substitute meal). Moreover, the
observed difference in willingness to buy and actual intake for
the blindfolded and non-blindfolded groups might have been
caused by differences in internal states of satiety. Both groups were
asked to refrain from eating for two hours before participation,
nonetheless the blindfolded group reported lower pre-testing hunger. However, including hunger as covariate in the analyses did not
yield a significant effect on the dependent variables, suggesting
that the internal need of hunger might not have been the only force
driving the observed approach behavior (see also Wansink &
Chandon, 2014).
Interestingly, the observed pattern of taste ratings seems to
support the concept of ‘hedonic-hunger’ (Lowe & Butryn, 2007),
that is, the drive to eat for pleasure in the absence of an energy deficit because the food has a high incentive value. The experienced
pleasure of eating (palatability, unpleasantness) was significantly
lower in the blindfolded group, as was the experienced refreshing
quality of the ice cream. Not seeing the food might have decreased
its incentive value, an idea that is corroborated by other studies
showing that visual cues such as color play an important role in
the eating experience (Jantathai, Sungsri-in, Mukprasirt, &
Duerrschmid, 2014; Spence, Levitan, Shankar, & Zampini, 2010)
and in the overall dining experience (Spence, 2010). The decrease
in ‘‘visual flavor” in the blindfolded condition (Spence &
Piqueras-Fiszman, 2012) might have decreased hedonic hunger
and, consequently, approach behavior.
Throughout most of human history, the discrimination of edible
and inedible food to avoid pathogens has been of primal
B. Renner et al. / Food Quality and Preference 50 (2016) 145–151
importance (Cockburn, 1971; Wolfe, Dunavan, & Diamond, 2007).
The robust elicitation of disgust when viewing spoiled and rotten
foods is considered as an evolutionary adaptation for that purpose
(e.g., Rozin & Fallon, 1987; Tybur, Lieberman, Kurzban, & DeScioli,
2013). Wansink and colleagues (2012) showed that ambiguous
(difficult to discern or identify) food is also rated as less acceptable
and willingness to consume it is lower. From an evolutionary
perspective this is an adaptive response because such ambiguity
could indicate an increased threat of ingesting pathogens (see also
Tuorila, Meiselman, Bell, Cardello, & Johnson, 1994). In the present
study, participants in the blindfolded condition were more surprised by and felt a greater need to get used to the ice cream’s taste
than the non-blindfolded group. These ratings are suggestive of
increased perceived food ambiguity, which may have lowered its
acceptability and the motivation to buy and consume it.
The findings regarding the reduced ability to monitor food
intake when blindfolded shed new light on the effect of visual
deprivation on intake perception. Both groups significantly overestimated the amount of ice cream they actually ate, which might
mirror the ‘bad calorie’ effect, the tendency to overestimate calories of foods that are perceived as unhealthy (Oakes, Sullivan, &
Slotterback, 2007, see also Chernev & Chandon, 2010; Wansink &
Chandon, 2006). However, while this bad calorie effect might
explain the general overestimation effect, it does not explain
why overestimation differed between the two groups as indicated
by the significant interaction term. Whereas the non-blindfolded
group overestimated intake by 35%, the blindfolded group overestimated intake by 88%. Interestingly, the blindfolded group
believed that they had eaten more ice cream than the nonblindfolded group when, in fact, their consumption was 9% lower.
Visual deprivation thus caused a pronounced dissociation between
actual and perceived intake. One might argue that the measurement of estimated consumption depends on visual information,
thus it could be that the large differences are also due to the fact
that it favors the non-blindfolded condition, limiting its validity
(we thank an anonymous reviewer for this suggestion). However,
it is important to note that the blindfolded participants systematically overestimated their intake rather than showing over- as well
as underestimations (thus, just a greater variance in their estimations) which would have indicated that participants had estimation problems due to missing visual information causing
disorientation. This pattern was not supported by the data, however; only evidence of systematic overestimation was found.
Hence, not seeing the food particularly seems to shift the threshold
for intake monitoring: smaller portions are sufficient to create the
same intake feeling. This notion of a shifted or more ‘conservative’
intake monitoring threshold aligns with findings reported by Linné
and colleagues (2002). They found that despite participants consuming a smaller amount of the test lunch meal when blindfolded,
their reported feeling of fullness was identical to that reported
after the meal consumed without blindfold. Although highly speculative, these results might indicate that vision deprivation
increases perceived intake because the estimation of the satiating
potential of foods (see Linné et al., 2002 and also Brunstrom &
Rogers, 2009) depends more on ‘real-time’ experience than on
prior expectations and thus ‘remembered’ experience (see
Kahneman, 2011 and Robinson, 2014).
Alternatively, this dissociation between actual and perceived
intake might be due to the fact that visual deprivation shifts attention to other senses. Research indicates that blind people show
better odor discrimination and identification (Cuevas, Plaza,
Rombaux, De Volder, & Renier, 2009) or superior tactile spatial acuity (Van Boven, Hamilton, Kauffman, Keenan, & Pascual-Leone,
2000) compared to sighted controls. The eating experience might
thus have been more intense under the blindfold condition, leading
to the observed overestimation effect (Spence & Piqueras-Fiszman,
149
2012). However, these findings might not be generalizable to
people who are deprived of vision only for a few minutes. The
dissociation might also be due to changes in the cephalic phase
of digestion and neural mechanism in the brain involved in the
termination of eating. Specifically, the sight of food facilitates the
cephalic phase of digestion (Blundell, Hill, & Lawton, 1989),
triggering salivation, insulin release, and gastric acid secretion,
which in turn affect neural mechanisms (Barkeling et al., 2003;
Linné et al., 2002, see also Simmons, Martin, & Barsalou, 2005;
van der Laan et al., 2011) and the motivation for consumption.
Scheibehenne and colleagues (2010) also assessed perceived
intake in a vision-deprivation study and, like in the current study,
found that participants’ ability to estimate their consumption deteriorated when eating blind. However, in their study, visual deprivation led to intake underestimation. This difference might be due to
the type of eating situation (taste test vs. full meal) and the food
being served (ice cream vs. lunch). Future studies might compare
the effect of visual deprivation on the consumption of ‘healthy’ versus ‘unhealthy’ food as well as main meals versus snacks. Moreover,
portion size as a normative cue (Herman & Polivy, 2008) might have
been stronger in the lunch situation realized by Scheibehenne and
colleagues (2010) as compared to the taste test paradigm utilized
in the present study. Finally, the two eating situations probably differed with regard to whether participants had their eyes open or
not. In the dining-in-the-dark restaurant participants probably ate
with their eyes open while in the present study using modified
ski goggles, participants probably had their eyes closed (see also
Spence & Piqueras-Fiszman, 2012). Eyes-open and eyes-closed
states in complete darkness differ consistently in the pattern of
associated brain activation. Ocular motor and attentional systems
are more activated when the eyes are open whereas the visual,
somatosensory, vestibular, and auditory system are more activated
when the eyes are closed (Marx et al., 2003; Wiesmann et al., 2006).
Thus, closing one’s eyes seems to induce a more interoceptive state
of awareness characterized by greater multisensory activity while
being in the dark, with the eyes open, induces an exeroceptive state
of awareness with greater ocular motor activity and attention
(Marx et al., 2003; Wiesmann et al., 2006).
4.1. Limitations
Limitations arise due to the specifics of the experimental procedure. A between-subjects design was chosen to prevent the inevitable order effects of a within-subject design. Hence, generalization is
limited and great caution is needed when drawing conclusions for
the real world (de Castro, 2000). Furthermore, confounding variables are of major concern. Importantly, control analyses secured
the main findings with respect to potential confounding variables
(hunger, outdoor temperature), but there might be other possible
confounders that have not been considered. Moreover, the present
study focused on one specific consumption situation in a student
sample exposed to experimentally controlled eating conditions.
Future research should examine the effects of vision deprivation
across different types of food, meals, and situations (see also
Sproesser, Kohlbrenner, Schupp, & Renner, 2015; Tăut, Renner, &
Baban, 2012). For example, one may speculate that the present findings extend to other eating situations where unhealthy food items
are consumed but not to eating situations with healthy food items.
Another potential limitation is in the method of assessing perceived consumption. For comparing actual and perceived intake
as indicators of intake monitoring, both variables need to be measured on the same metric. As grams were used in previous studies
to measure actual intake (see Scheibehenne et al., 2010), we opted
for grams as the measurement unit. In order to calibrate estimation
for all participants, we provided an anchor by stating that one
spoon typically contains 9 g of ice cream (see methods section).
150
B. Renner et al. / Food Quality and Preference 50 (2016) 145–151
This measurement might have favored the vision condition since
participants could see how full their spoons were each time
(we thank an anonymous reviewer for this suggestion). Although
we cannot exclude that the anchor may have been more useful
in the vision condition, the slightly greater variance within the
vision condition (SE = 23.6 g) than in the blindfolded condition
(SE = 19.5 g) does not suggest a differential facilitation effect. In
addition, if the method had facilitated a more accurate estimation
in the non-blindfolded condition, the blindfolded condition should
have been susceptible to greater estimation errors reflected in a
greater range of estimations including over- and underestimations.
Hence, the observed systematic intake overestimation might
rather indicate a shift in the threshold for intake monitoring. However, future studies are needed replicating this research without
providing such an anchor or by using alternative measures.
4.2. Conclusions and implications
The current study showed that depriving people of visual input
affects food-related perception and behavior across four different
response modes. Vision deprivation dissociated perceived consumption from actual consumption, with blindfolded participants
overestimating consumption to a much larger extent than nonblindfolded participants. Vision deprivation also affected taste
experiences and purchase willingness. Although results need to
be replicated across different types of food and situations, as
described above, these findings have two potential practical implications. First, they indicate that by removing sight it may be possible to shift the threshold for intake monitoring possibly by shifting
attention toward ‘interoceptive’ cues of eating (Marx et al., 2003).
This may provide unobtrusive and naturalistic means to change the
experience of eating behavior. Another important implication of
the finding that depriving participants from visual input dissociated their perceived from their actual eating behavior might be
that common cognitive based navigation systems for the food
environment such as dietary guidelines or nutrition facts which
are primarily cognitive based and typically lack sensory information might actually create a fragile intake monitoring. Hence, one
future perspective might be that we try to enrich the cognitive
input with sensory input to facilitate normal eating.
Declaration of conflicting interests
The authors declared that they had no conflicts of interest with
respect to their authorship or the publication of this article.
Acknowledgements
We thank Bettina Ott and Tobias Flaisch for creating the audio
questionnaire. We also thank Fee Benz, Kerstin Halbgebauer, and
Angela Whale for their valuable support. This research was supported by a grant from the Federal Ministry of Education and
Research (BMBF) (Grant 0315671, granted to Britta Renner & Harald Schupp). The funding body played no role in study design, in
collection, analysis and interpretation of data, in the writing of
the report, or in the decision to submit the article for publication.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.foodqual.2016.02.
010.
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